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Chemically modified attapulgite with asparagine for selective solid-phase extraction and preconcentration of Fe(III) from environmental samples
Analytica Chimica Acta 663 (2010) 213–217
Contents lists available at ScienceDirect
Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca
Chemically modified attapulgite with asparagine for selective solid-phase extraction and preconcentration of Fe(III) from environmental samples Zhipeng Zang a , Zhenhua Li a , Li Zhang a , Ruijun Li a , Zheng Hu a , Xijun Chang a,∗ , Yuemei Cui b a b
Department of Chemistry, Lanzhou University, Lanzhou 730000, PR China Jining Bureau of Quality and Technical Supervision, Jining 272000, PR China
a r t i c l e
i n f o
Article history: Received 17 October 2009 Received in revised form 18 January 2010 Accepted 28 January 2010 Available online 6 February 2010 Keywords: Modified attapulgite Asparagine Iron determination Solid-phase extraction Inductively coupled plasma optical emission spectrometry
a b s t r a c t A new method that utilizes asparagine modified attapulgite as a solid phase extractant has been developed for preconcentration of trace Fe(III) prior to the measurement by inductively coupled plasma optical emission spectrometry. Characterization of the surface modification was performed on the basis of Fourier transform infrared spectra. The separation/preconcentration conditions of the analyte were investigated, including the pH value, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the new adsorbent had relatively high capacity and enrichment factor compared to other methods reported so far. The adsorbed Fe(III) was quantitatively eluted by 2 mL of 0.5 mol L−1 HCl. Common coexisting ions did not interfere with the separation. The detection limit of the method was 0.19 g L−1 . The relative standard deviation was 3.4% (n = 8) which indicated that the method had good precision for the analysis of trace Fe(III) in solution samples. The method was validated using two certified reference materials and has been applied for the determination of trace Fe(III) in biological and natural water samples with satisfactory results. © 2010 Elsevier B.V. All rights reserved.
1. Introduction In recent years, the extraction and determination processes of trace metal ions or species from different matrices especially aqueous samples have become of paramount importance and have received more and more attention. Fe(III) is known as one of the essential trace metals for many living organisms [1] and it is important to determine trace amounts of iron in water for environmental protection, hydrogeology and some chemical processes. Therefore, it is crucial to develop simple, rapid, and efficient methods for monitoring iron in the environment. The most widely used methods for analyzing metal ions are inductively coupled plasma optical emission spectrometry (ICP-OES) and atomic absorption spectrometry (AAS), but their sensitivity and selectivity are usually insufficient for direct determination of these contaminants at a very low concentration level in complex matrix environmental samples. Therefore, a sample separation/preconcentration step prior to analysis is usually necessary. Solid-phase extraction (SPE) is one of the most common techniques used for preconcentration of analytes in environmental water because of its advantages of high enrichment factor, high
∗ Corresponding author. Tel.: +86 931 891 2422; fax: +86 931 891 2582. E-mail address: li [email protected] (X. Chang). 0003-2670/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2010.01.057
recovery, rapid phase separation, low cost, low consumption of organic solvents and the ability of combination with different detection techniques in the form of on-line or off-line mode [2]. In SPE procedures, the choice of the appropriate adsorbent is a critical factor to obtain full recovery and high enrichment factor [3,4]. Attapulgite (ATP, or palygorskite) is a hydrated magnesium aluminum silicate present in nature as fibrillar mineral [5,6]. Since the time its ideal structure was studied by Bradley in 1940 they have come under intense multidisciplinary study because of their unique physical and chemical properties and their possible applications. Attapulgite and activated attapulgite, which is a natural, cheap, adsorbent clay mineral with exchangeable cations and reactive-OH groups on its surface [7], have been intensively used as adsorbents for the removal of heavy metal ions [8–11] and organic contaminants [12,13]. However, the adsorption capacity and selectivity of attapulgite and activated attapulgite for SPE is quite limited, especially for metal ions. For this reason, modification and impregnation techniques have long been used to increase the surface adsorption and add selectivity of attapulgite. There are several recent reports on the use of modified attapulgite for metal enrichment. Attapulgite functionalized with 2,2-bis(hydroxymethyl)propionic acid [14], ammonium citrate tribasic [15] and polyacrylamide [16] is reported as a chelating collector for metal ions. The modified attapulgite exhibits selectivity and adsorption capacities higher than untreated attapulgite.
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In our work, attapulgite was modified by asparagine (ASP) to improve the surface properties and adsorption capacity. The new adsorbent presented high selectivity and adsorption capacity for the solid-phase extraction of Fe(III). Parameters that can affect the adsorption and elution efficiency of Fe(III) were studied in batch and column modes. Then, the method was validated by analyzing the standard reference materials (GBW 08301, river sediment; GBW 08504, cabbage) and applied to the analysis of biological and water samples with satisfactory results. 2. Experimental 2.1. Chemicals and reagents Reagents of analytical and spectral purity were used for all experiments and doubly distilled deionized water was used throughout. Standard labware and glassware used were repeatedly cleaned with HNO3 and rinsed with double distilled water, according to a published procedure [17]. Standard stock solution of Fe(III) (1 mg mL−1 ) were prepared by dissolving spectral pure grade chemical FeCl3 ·6H2 O (The First Reagent Factory, Shanghai, China) in double-distilled water with the addition of hydrochloric acid (The First Reagent Factory, Shanghai, China) and further diluted daily prior to use. Attapulgite (ATP) with the average diameter of 325 meshes was provided by Gansu ATP Co. Ltd., Gansu, China. It was dried in vacuum at 110 ◦ C for 48 h before use. Asparagine (Beijing Chemical Industry, Beijing, China) and 3-aminopropyltrimethoxysilane (Chemical Engineering Corporation of Ocean University of China, Qingdao, China) were used in this work. N,N’-dicyclohexylcarbodiimide (DCC) was purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). The standard reference materials (GBW 08301, river sediment; GBW 08504, cabbage) were provided by the National Research Center for Certified Reference Materials (Beijing, China). 2.2. Instruments and apparatus An Iris Advantage ER/S inductively coupled plasma emission spectrometer, Thermo Jarrel Ash (Franklin, MA, USA) was used for determination of all metal ions. The instrumental parameters were those recommended by the manufacturer. The wavelength selected for Fe was 259.940 nm. A pHs-3C digital pH meter (Shanghai Lei Ci Device Works, Shanghai, China) was used for the pH adjustments. Infrared spectra (4000–400 cm−1 ) in KBr were recorded on a Nicolet NEXUS 670 Fourier transform infrared (FT-IR) spectrometer (Nicolet, Madison, WI, USA). A YL-110 peristaltic pump (General Research Institute for Non-ferrous Metals, Beijing, China) was used in the column process. A PTFE (polytetrafluoroethylene) column
(50 mm × 9.0 mm i.d.; Tianjin Jinteng Instrument Factory, Tianjin, China) was used.
2.3. Sample preparation River water was collected from the Yellow River, Lanzhou, China. The water samples were filtered through a 0.45 m PTFE millipore filter, and acidified to a pH of about 2 with concentrated HCl prior to storage for use. Tap water samples taken from our research laboratory were analyzed without pretreatment. The pH value was adjusted to 2 with 0.1 mol L−1 HCl prior to storage for use. Balsam pear leaves were obtained from Anning village, Lanzhou, China. Balsam pear leaves were dried in an oven at 80 ◦ C to a constant weight. 1.0 g of balsam pear leaves sample was weighed and transferred into a digestion tube, and then 5 mL of concentrated HNO3 was added into it. The tube was left at room temperature for one night. Then it was placed in a digester block and heated slowly until the temperature was up to 165 ◦ C. This temperature was maintained until the evolution of the brown fumes ceased. After the tube was cooled down, 1.3 mL of perchloric acid was added into it. Then the temperature was raised to 210 ◦ C until evolution of white fumes began. The volume was adjusted to 100 mL with double-distilled water when the tube was cooled down [18]. The standard reference materials (GBW 08301, river sediment; GBW 08504, cabbage) were digested according to literature [19].
2.4. Synthesis 2.4.1. Synthesis of attapulgite-bound amine Attapulgite was first purified and activated with HCl (3.0 mol L−1 ) at 70 ◦ C for 3 h, then filtrated and repeatedly washed with water until the filtrate is neutral, then dried in an oven at 160 ◦ C for 8 h to remove surface-adsorbed water. In order to prepare attapulgite-bound amine (ATPAP), 10.0 g of purified attapulgite was suspended in 150 mL dry toluene containing 10 mL of 3-aminopropyltrimethoxysilane and refluxed over night. The product (ATPAP) was filtered off, washed with toluene, ethanol and diethyl ether and dried in an oven at 60 ◦ C for 6 h.
2.4.2. Synthesis of asparagine modified attapulgite (ATP–ASP) For the synthesis of ATP–ASP, a 5.0 g amount of ATPAP was suspended in 250 mL of dry ethanol under stirring and heating, then 1.0 g of asparagine was added into the suspension and refluxed for 12 h. The product (ATP–ASP) was filtered off, washed with ethanol and dried in an oven at 80 ◦ C for 8 h. The synthesis route of ATP–ASP is illustrated in Fig. 1.
Fig. 1. Synthesis route of ATP–ASP.
Z. Zang et al. / Analytica Chimica Acta 663 (2010) 213–217
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2.5. Procedures 2.5.1. Batch method A series of standards or sample solutions containing Fe(III) were transferred into a 25 mL beaker, and the pH value was adjusted to the desired value with 0.1 mol L−1 HCl and 0.1 mol L−1 NH3 . Then the volume was adjusted to 10 mL with double-distilled water. Twentyfive milligrams of ATP–ASP was added, and the mixture was shaken vigorously for 20 min to facilitate adsorption of the metal ions onto the adsorbents. The concentrations of the metal ions in the solution were directly determined by inductively coupled plasma optical emission spectrometry (ICP-OES). 2.5.2. Column SPE procedure Fifty milligrams of ATP–ASP was packed in the PTFE column plugged with a small portion of glass wool at both ends. Before use, 0.5 mol L−1 HCl and double-distilled deionized water were successively passed through the microcolumn in order to equilibrate, clean and neutralize it. Portions of aqueous standard or sample solutions containing Fe(III) were prepared, and the pH value was adjusted to the desired pH value with 0.10 mol L−1 HCl or 0.10 mol L−1 NH3 . Each solution was passed through the column at a flow rate of 2.5 mL min−1 by a peristaltic pump. Afterwards, the metal ions retained on the column were eluted with 0.5 mol L−1 HCl and the analytes in the eluate were determined by ICP-OES. 3. Results and discussion 3.1. FT-IR spectra The FT-IR spectra of ATP, ATPAP and ATP–ASP are shown in Fig. 2. .According to the FT-IR spectrum of ATP, the peaks at 3617 and 3541 cm−1 correspond to the stretching vibrations of the Al-OH unit. The peaks at 1026 and 470 cm−1 are attributed to Si–O–Si bonds. The peak at 780 cm−1 may correspond to the stretching vibration of Al–O–Si. The peak at 1652 cm−1 corresponds to the bending vibration of zeolite water [20]. Comparison of the
Fig. 2. FT-IR spectra of ATP (a), ATPAP (b) and ATP–ASP (c).
Fig. 3. Effect of pH on adsorption of 1.0 g mL−1 Fe(III) on ATP–ASP. Other conditions: shaking time 20 min, temperature 25 ◦ C.
FT-IR spectrum of ATPAP with ATP showed that the new peak (1563 cm−1 ) appearing in ATPAP is due to N–H bending vibration and the peak at 3323 cm−1 is caused by N–H stretching vibration, which indicated that the attapulgite-bound amine was prepared successfully. When ATPAP was modified by ASP, several new peaks appeared in the spectrum. According to the literature [21,22], the new peaks can be assigned as follows: the peak at 1680 cm−1 is due to C = O stretching vibration. The peak at 1612 cm−1 is caused by N–H bending vibration. The peak at 1247 cm−1 is due to C–N stretching vibration and the bands around 3558 cm−1 can be assigned to N–H stretching vibration. Consequently, the above experimental results suggest that ATP was successfully modified by ASP. 3.2. Batch method procedure 3.2.1. Effect of pH on adsorption of Fe(III) According to the recommended procedure (batch method), ten metal ions, viz. Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) were determined at different pH values, namely pH 1, 2, 3, 4, 5, 6 and 7. Aliquots of 10 mL of the solutions were tested by equilibrating 25 mg of the adsorbent. The adsorption experiments were in triplicates. Finally, Fe(III) was found to be the only metal ion highly extracted by ATP–ASP. As can be seen from Fig. 3, the adsorption quantity of Fe(III) increases with the increase of pH value in the studied pH ranges. Below pH 2.0, the adsorption quantity of Fe(III) was very low which is attributed to the protonation of the adsorbent, but the adsorption rate is increasing rapidly above pH 2.0; above pH 4.0, the adsorption quantity remained relatively constant. Owing to hydrolysis at higher pH value, pH 4 was chosen as the optimum pH for further studies. In addition, Cu(II), Co(II), Ni(II), Zn(II) and Mn(II) were not enriched by ATP–ASP at pH 4; Fe(II) could be adsorbed only to an extent of approximately 15%. Pb(II), Cd(II), Cr(III) and Hg(II) could be adsorbed by ATP–ASP in a range of 40–80% at pH 4, but they do not interfere with enrichment and determination of Fe(III). 3.2.2. Effect of the mass of adsorbent To test the effect of the mass of adsorbent on quantitative retention of Fe(III), different amounts of ATP–ASP (range from 5 to 40 mg) were added into the solution following the experimental method. The results showed that quantitative adsorption for Fe(III) was obtained in the range of 25–40 mg of ATP–ASP. Quantitative adsorption was not obtained when the mass of extractant was smaller than 25 mg. So 25 mg of ATP–ASP was selected for further studies.
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Table 1 Elution recovery (%) for Fe(III) adsorbed on ATP–ASP. Optimization of eluent concentration (the volume of HCl was 10 mL) Concentration (mol L−1 ) 0.01 0.05 Recovery (%) 27.6 64.9
0.1 90.9
0.5 100.0
1 100.3
2 99.9
Optimization of eluent volume (the concentration of HCl was 0.5 mol L−1 ) Volume (mL) 1.0 2.0 Recovery (%) 80.6 100.2
3.0 99.7
4.0 100.0
5.0 99.6
6.0 99.7
3.2.3. Effect of shaking time Shaking time is an important factor in determining the possibility of application of ATP–ASP for the selective extraction of metal ions. In this work, different shaking times (range from 5 to 40 min) were studied for the percentage extraction of Fe(III) by ATP–ASP. The results showed that the adsorption of Fe(III) was over 90% sorption during the first 10 min. It indicated that kinetics of equilibrium are very fast. The reasonably rapid kinetics of ATP–ASP–Fe(III) interaction at pH 4 reflected the high affinity and selectivity of ATP–ASP for Fe(III). We select 20 min for further studies. 3.3. Column SPE procedure 3.3.1. Effect of elution condition on recovery Since the adsorption of Fe(III) at pH < 2 is negligible, we can expect that elution will be favored in acidic solution. For this reason, various concentrations and volumes of HCl were used for the desorption of retained Fe(III). It was found from Table 1 that 2 mL of 0.50 mol L−1 HCl was sufficient for the complete elution of Fe(III). So 2 mL of 0.50 mol L−1 HCl was used as eluent in the following experiments. 3.3.2. Effect of flow rate In an SPE system, the flow rate of sample solution not only affects the recoveries of analytes, but also controls the analysis time. Therefore, the effect of the flow rate of sample solution was examined under the optimum conditions (pH, eluent, etc.) by passing 50 mL of sample solution through the microcolumn with a peristaltic pump. The flow rate was adjusted in a range of 0.5 to 5.0 mL min−1 . It was found that the retention of Fe(III) was practically not changed up to 2.5 mL min−1 flow rate. The recovery of Fe(III) decreased slightly when the flow rate is over 2.5 mL min−1 . Thus, a flow rate of 2.5 mL min−1 is employed in this work. 3.3.3. Maximum sample volume and enrichment factor To obtain reliable and reproducible analytical results and a high concentration factor, it is very important to get satisfactory recoveries for all the compounds studied in as large a volume of sample solutions as possible. So it is necessary to obtain the maximum volume in the SPE. To determine the maximum volume, different volumes of purified water at pH 4.0 were spiked with Fe(III) at 1.0 g mL −1 concentration levels. Following the experimental procedure, the recoveries of analyte at different volumes were obtained. The results showed that the maximum sample volume could be up to 400 mL with the recovery >95%. Therefore, 400 mL of sample solution was adopted for the preconcentration of Fe(III) from sample solutions. A high enrichment factor of 200
Fig. 4. Effect of initial volume (V0 ) of Fe(III) on the adsorption quantity (Q) of ATP–ASP. pH 4.0; sample concentration 10 g mL−1 ; temperature 25 ◦ C.
was obtained because 2.0 mL of 0.5 mol L−1 HCl was used as eluent in these experiments. 3.4. Adsorption capacity The adsorption capacity is an important factor because it determines how much adsorbent is required to quantitatively concentrate the analytes from a given solution. The adsorption capacity was tested following the general procedure. To measure the static adsorption capacity, 50 mg of adsorbent was treated with 10.0 g mL−1 of various volumes of Fe(III) solutions adjusted with 0.1 mol L−1 of HCl or NH3 at pH 4. As can be seen in Fig. 4, the amount of Fe(III) adsorbed per unit mass of ATP–ASP increased with the initial volume of Fe(III). The initial volume of Fe(III) was increased till the plateau values (adsorption capacity values) were obtained. The static adsorption capacity of ATP–ASP for Fe(III) was calculated as 33.63 mg g−1 . However, Fe(III) was adsorbed poorly on untreated attapulgite and ATPAP at pH 4. The adsorption capacity and enrichment factor of ATP–ASP for Fe(III) were also compared with those of other important matrices used for the separation and preconcentration (Table 2). As seen from the data, ATP–ASP had relatively high capacity and enrichment factor values compared to other methods reported. 3.5. Effects of coexisting ions The effects of common coexisting ions on the adsorption of Fe(III) on ATP–ASP were investigated. In these experiments, solu-
Table 2 Comparison of adsorption capacity and enrichment factor of some adsorbents used for the separation and preconcentration of Fe(III). Adsorbent
Complexing media
Capacity
Enrichment factor
Reference
Nanometer SiO2 Multiwalled carbon nanotubes Silica gel Naphthalene Sepiolite Attapulgite
P-dimethylamino benzaldehyde Ethylenediamine Curcumin Methylthymol blue Escherichia coli Asparagine
14.7 mg g−1 28.69 mg g−1 0.46 mmol g−1 0.10 mg g−1 0.098 mmol g−1 33.63 mg g−1 (0.60 mmol g−1 )
100 200 75 100 50 200
[23] [24] [25] [26] [27] Present work
Z. Zang et al. / Analytica Chimica Acta 663 (2010) 213–217 Table 3 Analysis results for the determination of Fe(III) in standard reference materials (GBW 08301, river sediment; GBW 08504, cabbage) and biological samples. Analyte
Measured (g g-1 )a
Certified (g g-1 )
GBW08301 GBW08504 Balsam pear leaves
39.8 ± 1.3 52.1 ± 1.8 3.58 ± 0.22
39.4 ± 0.12 52.0 ± 3.2 3.56 ± 0.17
a
The value following “ ± ” is the standard deviation (n = 3).
Table 4 Analytical results for the determination of Fe(III) in Yellow River and tap water samples. Ion
Added
Founda
0
4.32 ± 0.05 9.54 ± 0.16 14.51 ± 0.07 0.13 ± 0.05 5.11 ± 0.06 10.05 ± 0.10
Recovery (%)
−1
Fe (III) (g mL ) Yellow River water
Tap water
a
5 10 0 5 10
102.4 101.3 99.6 99.2
The value following “ ± ” is the standard deviation (n = 5).
tions of 1.0 g mL−1 of Fe(III) containing the added interfering ions were treated according to the recommended procedure. The tolerance limit was set as the amount of ions causing recoveries of the analyte to be less than 90%. The results showed that in excess of 2000-fold K(I), Na(I), Ca(II) and Mg(II), 100-fold Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Cr(III), Pb(II) and Hg(II) ions had no significant interferences in the preconcentration and determination of Fe(III). This is due to the low adsorbing capacity or rates for interfering ions. It can be seen that the presence of major coexisting ions has no obvious influence on the determination of Fe(III) under the selected conditions. 3.6. Detection limits and precision Under the optimal conditions, eight portions of standard solutions were enriched and analyzed simultaneously following the recommended procedure. The relative standard deviation (RSD) of the method was 3.4%, which indicated that the method has good precision for the analysis of trace Fe(III) in solution samples. In accordance with the definition of IUPAC, the detection limit of the method was calculated based on three times the standard deviation of eight runs of the blank solution. The detection limit (3) of the proposed method was 0.19 g L−1 . 3.7. Application of the method The proposed method has been applied to the determination of trace Fe(III) in standard materials (GBW 08301, river sediment; GBW 08504, cabbage), balsam pear leaves, tap water and Yellow River water samples. The results are listed in Tables 3 and 4. The
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analytical results for the standard materials were in good agreement with the certified values. The analytical results for balsam pear leaves were in agreement with the electrothermal atomic absorption spectrometry (ET-AAS) method. For the analysis of natural Yellow River water and tap water samples, the standard addition method was used. The recoveries of analyte were in the range of 99–103%. These results indicated the suitability of ATP–ASP for selective SPE and determination of trace Fe(III) in environmental samples. 4. Conclusions In this study, the proposed selective and sensitive method for the determination of trace Fe(III) was developed by using asparagine modified attapulgite as solid-phase extractant. The preparation of asparagine modified attapulgite sorbent was relatively simple and rapid. This new adsorbent had higher adsorption capacity and selectivity for Fe(III), and the method was successfully applied to the analysis of trace Fe(III) in biological and water samples. The precision and accuracy of the method are satisfactory. References [1] J.H. Martin, S.E. Fritzwater, Nature 331 (1988) 342–343. [2] K. Pyrzynska, Crit. Rev. Anal. Chem. 29 (1999) 313–321. [3] C.F. Poole, New trends in solid-phase extraction, Trends Anal. Chem. 22 (2003) 362–373. [4] J.R. Dean, Extraction Methods for Environmental Analysis, Wiley, New York, 1998. [5] R. Giustetto, F.X.L. Xamena, G. Ricchiardi, S. Bordiga, A. Damin, R. Gobetto, M.R. Chierotti, J. Phys. Chem. B 109 (2005) 19360–19368. [6] J. Huang, Y. Liu, Q. Jin, X. Wang, J. Yang, J. Hazard. Mater. 143 (2007) 541–548. [7] A. Neaman, A. Singer, Appl. Clay Sci. 25 (2004) 121–124. [8] E. Álvarez-Ayuso, A. García-Sánchez, J. Hazard. Mater. 147 (2007) 594–600. [9] H. Chen, A.Q. Wang, J. Colloid Interface Sci. 307 (2007) 309–316. [10] H. Chen, Y.G. Zhao, A.Q. Wang, J. Hazard. Mater. 149 (2007) 346–354. [11] W.J. Wang, H. Chen, A.Q. Wang, Sep. Purif. Technol. 55 (2007) 157–164. [12] H.H. Murray, Appl. Clay Sci. 17 (2000) 207–211. [13] K. Boki, K. Sakaguchi, H. Tomioka, JJTHE 41 (1995) 426–432. [14] P. Liu, T.M. Wang, J. Hazard. Mater. 149 (2007) 75–79. [15] Q.H. Fan, D.D. Shao, J. Hu, W.S. Wu, X.K. Wang, Surf. Sci. 602 (2008) 778–785. [16] Y.J. Zhao, Y. Chen, M.S. Li, S.Y. Zhou, A.L. Xue, W.H. Xing, J. Hazard. Mater. 171 (2009) 640–646. [17] D.P.H. Laxen, R.M. Harrison, Anal. Chem. 53 (1981) 345–350. [18] E.S. Miranda Carlos, B.F. Reis, N. Baccan, A.P. Packer, M.F. Gine, Anal. Chim. Acta 453 (2002) 301–310. [19] Y.W. Liu, X.J. Chang, Y. Guo, S.M. Meng, J. Hazard. Mater. B 135 (2006) 389–394. [20] Z.W. Niu, Q.H. Fan, W.H. Wang, J.Z. Xu, L. Chen, W.S. Wu, Appl. Radiat. Isot. 67 (2009) 1582–1590. [21] H.T. Tang, Organic Compound Spectra Determination, Publishing house of Beijing University, Beijing, 1992, pp. 124-159. [22] Q.N. Dong, IR Spectrum Method, Publishing house of the Chemical Industry, Beijing, 1979, pp. 104–168. [23] Y.M. Cui, X.J. Chang, Y.H. Zhai, X.B. Zhu, H. Zheng, N. Lian, Microchem. J. 83 (2006) 35–41. [24] Z.P. Zang, Z. Hu, Z.H. Li, Q. He, X.J. Chang, J. Hazard. Mater. 172 (2009) 958–963. [25] X.B. Zhu, X.J. Chang, Y.M. Cui, X.J. Zou, D. Yang, Z. Hu, Microchem. J. 86 (2007) 189–194. [26] N. Pourreza, R. Hoveizavi, Anal. Chim. Acta 549 (2005) 124–128. [27] H. Bag, A.R. Turker, M. Lale, Talanta 51 (2000) 1035–1043.
Contents lists available at ScienceDirect
Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca
Chemically modified attapulgite with asparagine for selective solid-phase extraction and preconcentration of Fe(III) from environmental samples Zhipeng Zang a , Zhenhua Li a , Li Zhang a , Ruijun Li a , Zheng Hu a , Xijun Chang a,∗ , Yuemei Cui b a b
Department of Chemistry, Lanzhou University, Lanzhou 730000, PR China Jining Bureau of Quality and Technical Supervision, Jining 272000, PR China
a r t i c l e
i n f o
Article history: Received 17 October 2009 Received in revised form 18 January 2010 Accepted 28 January 2010 Available online 6 February 2010 Keywords: Modified attapulgite Asparagine Iron determination Solid-phase extraction Inductively coupled plasma optical emission spectrometry
a b s t r a c t A new method that utilizes asparagine modified attapulgite as a solid phase extractant has been developed for preconcentration of trace Fe(III) prior to the measurement by inductively coupled plasma optical emission spectrometry. Characterization of the surface modification was performed on the basis of Fourier transform infrared spectra. The separation/preconcentration conditions of the analyte were investigated, including the pH value, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the new adsorbent had relatively high capacity and enrichment factor compared to other methods reported so far. The adsorbed Fe(III) was quantitatively eluted by 2 mL of 0.5 mol L−1 HCl. Common coexisting ions did not interfere with the separation. The detection limit of the method was 0.19 g L−1 . The relative standard deviation was 3.4% (n = 8) which indicated that the method had good precision for the analysis of trace Fe(III) in solution samples. The method was validated using two certified reference materials and has been applied for the determination of trace Fe(III) in biological and natural water samples with satisfactory results. © 2010 Elsevier B.V. All rights reserved.
1. Introduction In recent years, the extraction and determination processes of trace metal ions or species from different matrices especially aqueous samples have become of paramount importance and have received more and more attention. Fe(III) is known as one of the essential trace metals for many living organisms [1] and it is important to determine trace amounts of iron in water for environmental protection, hydrogeology and some chemical processes. Therefore, it is crucial to develop simple, rapid, and efficient methods for monitoring iron in the environment. The most widely used methods for analyzing metal ions are inductively coupled plasma optical emission spectrometry (ICP-OES) and atomic absorption spectrometry (AAS), but their sensitivity and selectivity are usually insufficient for direct determination of these contaminants at a very low concentration level in complex matrix environmental samples. Therefore, a sample separation/preconcentration step prior to analysis is usually necessary. Solid-phase extraction (SPE) is one of the most common techniques used for preconcentration of analytes in environmental water because of its advantages of high enrichment factor, high
∗ Corresponding author. Tel.: +86 931 891 2422; fax: +86 931 891 2582. E-mail address: li [email protected] (X. Chang). 0003-2670/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2010.01.057
recovery, rapid phase separation, low cost, low consumption of organic solvents and the ability of combination with different detection techniques in the form of on-line or off-line mode [2]. In SPE procedures, the choice of the appropriate adsorbent is a critical factor to obtain full recovery and high enrichment factor [3,4]. Attapulgite (ATP, or palygorskite) is a hydrated magnesium aluminum silicate present in nature as fibrillar mineral [5,6]. Since the time its ideal structure was studied by Bradley in 1940 they have come under intense multidisciplinary study because of their unique physical and chemical properties and their possible applications. Attapulgite and activated attapulgite, which is a natural, cheap, adsorbent clay mineral with exchangeable cations and reactive-OH groups on its surface [7], have been intensively used as adsorbents for the removal of heavy metal ions [8–11] and organic contaminants [12,13]. However, the adsorption capacity and selectivity of attapulgite and activated attapulgite for SPE is quite limited, especially for metal ions. For this reason, modification and impregnation techniques have long been used to increase the surface adsorption and add selectivity of attapulgite. There are several recent reports on the use of modified attapulgite for metal enrichment. Attapulgite functionalized with 2,2-bis(hydroxymethyl)propionic acid [14], ammonium citrate tribasic [15] and polyacrylamide [16] is reported as a chelating collector for metal ions. The modified attapulgite exhibits selectivity and adsorption capacities higher than untreated attapulgite.
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In our work, attapulgite was modified by asparagine (ASP) to improve the surface properties and adsorption capacity. The new adsorbent presented high selectivity and adsorption capacity for the solid-phase extraction of Fe(III). Parameters that can affect the adsorption and elution efficiency of Fe(III) were studied in batch and column modes. Then, the method was validated by analyzing the standard reference materials (GBW 08301, river sediment; GBW 08504, cabbage) and applied to the analysis of biological and water samples with satisfactory results. 2. Experimental 2.1. Chemicals and reagents Reagents of analytical and spectral purity were used for all experiments and doubly distilled deionized water was used throughout. Standard labware and glassware used were repeatedly cleaned with HNO3 and rinsed with double distilled water, according to a published procedure [17]. Standard stock solution of Fe(III) (1 mg mL−1 ) were prepared by dissolving spectral pure grade chemical FeCl3 ·6H2 O (The First Reagent Factory, Shanghai, China) in double-distilled water with the addition of hydrochloric acid (The First Reagent Factory, Shanghai, China) and further diluted daily prior to use. Attapulgite (ATP) with the average diameter of 325 meshes was provided by Gansu ATP Co. Ltd., Gansu, China. It was dried in vacuum at 110 ◦ C for 48 h before use. Asparagine (Beijing Chemical Industry, Beijing, China) and 3-aminopropyltrimethoxysilane (Chemical Engineering Corporation of Ocean University of China, Qingdao, China) were used in this work. N,N’-dicyclohexylcarbodiimide (DCC) was purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). The standard reference materials (GBW 08301, river sediment; GBW 08504, cabbage) were provided by the National Research Center for Certified Reference Materials (Beijing, China). 2.2. Instruments and apparatus An Iris Advantage ER/S inductively coupled plasma emission spectrometer, Thermo Jarrel Ash (Franklin, MA, USA) was used for determination of all metal ions. The instrumental parameters were those recommended by the manufacturer. The wavelength selected for Fe was 259.940 nm. A pHs-3C digital pH meter (Shanghai Lei Ci Device Works, Shanghai, China) was used for the pH adjustments. Infrared spectra (4000–400 cm−1 ) in KBr were recorded on a Nicolet NEXUS 670 Fourier transform infrared (FT-IR) spectrometer (Nicolet, Madison, WI, USA). A YL-110 peristaltic pump (General Research Institute for Non-ferrous Metals, Beijing, China) was used in the column process. A PTFE (polytetrafluoroethylene) column
(50 mm × 9.0 mm i.d.; Tianjin Jinteng Instrument Factory, Tianjin, China) was used.
2.3. Sample preparation River water was collected from the Yellow River, Lanzhou, China. The water samples were filtered through a 0.45 m PTFE millipore filter, and acidified to a pH of about 2 with concentrated HCl prior to storage for use. Tap water samples taken from our research laboratory were analyzed without pretreatment. The pH value was adjusted to 2 with 0.1 mol L−1 HCl prior to storage for use. Balsam pear leaves were obtained from Anning village, Lanzhou, China. Balsam pear leaves were dried in an oven at 80 ◦ C to a constant weight. 1.0 g of balsam pear leaves sample was weighed and transferred into a digestion tube, and then 5 mL of concentrated HNO3 was added into it. The tube was left at room temperature for one night. Then it was placed in a digester block and heated slowly until the temperature was up to 165 ◦ C. This temperature was maintained until the evolution of the brown fumes ceased. After the tube was cooled down, 1.3 mL of perchloric acid was added into it. Then the temperature was raised to 210 ◦ C until evolution of white fumes began. The volume was adjusted to 100 mL with double-distilled water when the tube was cooled down [18]. The standard reference materials (GBW 08301, river sediment; GBW 08504, cabbage) were digested according to literature [19].
2.4. Synthesis 2.4.1. Synthesis of attapulgite-bound amine Attapulgite was first purified and activated with HCl (3.0 mol L−1 ) at 70 ◦ C for 3 h, then filtrated and repeatedly washed with water until the filtrate is neutral, then dried in an oven at 160 ◦ C for 8 h to remove surface-adsorbed water. In order to prepare attapulgite-bound amine (ATPAP), 10.0 g of purified attapulgite was suspended in 150 mL dry toluene containing 10 mL of 3-aminopropyltrimethoxysilane and refluxed over night. The product (ATPAP) was filtered off, washed with toluene, ethanol and diethyl ether and dried in an oven at 60 ◦ C for 6 h.
2.4.2. Synthesis of asparagine modified attapulgite (ATP–ASP) For the synthesis of ATP–ASP, a 5.0 g amount of ATPAP was suspended in 250 mL of dry ethanol under stirring and heating, then 1.0 g of asparagine was added into the suspension and refluxed for 12 h. The product (ATP–ASP) was filtered off, washed with ethanol and dried in an oven at 80 ◦ C for 8 h. The synthesis route of ATP–ASP is illustrated in Fig. 1.
Fig. 1. Synthesis route of ATP–ASP.
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2.5. Procedures 2.5.1. Batch method A series of standards or sample solutions containing Fe(III) were transferred into a 25 mL beaker, and the pH value was adjusted to the desired value with 0.1 mol L−1 HCl and 0.1 mol L−1 NH3 . Then the volume was adjusted to 10 mL with double-distilled water. Twentyfive milligrams of ATP–ASP was added, and the mixture was shaken vigorously for 20 min to facilitate adsorption of the metal ions onto the adsorbents. The concentrations of the metal ions in the solution were directly determined by inductively coupled plasma optical emission spectrometry (ICP-OES). 2.5.2. Column SPE procedure Fifty milligrams of ATP–ASP was packed in the PTFE column plugged with a small portion of glass wool at both ends. Before use, 0.5 mol L−1 HCl and double-distilled deionized water were successively passed through the microcolumn in order to equilibrate, clean and neutralize it. Portions of aqueous standard or sample solutions containing Fe(III) were prepared, and the pH value was adjusted to the desired pH value with 0.10 mol L−1 HCl or 0.10 mol L−1 NH3 . Each solution was passed through the column at a flow rate of 2.5 mL min−1 by a peristaltic pump. Afterwards, the metal ions retained on the column were eluted with 0.5 mol L−1 HCl and the analytes in the eluate were determined by ICP-OES. 3. Results and discussion 3.1. FT-IR spectra The FT-IR spectra of ATP, ATPAP and ATP–ASP are shown in Fig. 2. .According to the FT-IR spectrum of ATP, the peaks at 3617 and 3541 cm−1 correspond to the stretching vibrations of the Al-OH unit. The peaks at 1026 and 470 cm−1 are attributed to Si–O–Si bonds. The peak at 780 cm−1 may correspond to the stretching vibration of Al–O–Si. The peak at 1652 cm−1 corresponds to the bending vibration of zeolite water [20]. Comparison of the
Fig. 2. FT-IR spectra of ATP (a), ATPAP (b) and ATP–ASP (c).
Fig. 3. Effect of pH on adsorption of 1.0 g mL−1 Fe(III) on ATP–ASP. Other conditions: shaking time 20 min, temperature 25 ◦ C.
FT-IR spectrum of ATPAP with ATP showed that the new peak (1563 cm−1 ) appearing in ATPAP is due to N–H bending vibration and the peak at 3323 cm−1 is caused by N–H stretching vibration, which indicated that the attapulgite-bound amine was prepared successfully. When ATPAP was modified by ASP, several new peaks appeared in the spectrum. According to the literature [21,22], the new peaks can be assigned as follows: the peak at 1680 cm−1 is due to C = O stretching vibration. The peak at 1612 cm−1 is caused by N–H bending vibration. The peak at 1247 cm−1 is due to C–N stretching vibration and the bands around 3558 cm−1 can be assigned to N–H stretching vibration. Consequently, the above experimental results suggest that ATP was successfully modified by ASP. 3.2. Batch method procedure 3.2.1. Effect of pH on adsorption of Fe(III) According to the recommended procedure (batch method), ten metal ions, viz. Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) were determined at different pH values, namely pH 1, 2, 3, 4, 5, 6 and 7. Aliquots of 10 mL of the solutions were tested by equilibrating 25 mg of the adsorbent. The adsorption experiments were in triplicates. Finally, Fe(III) was found to be the only metal ion highly extracted by ATP–ASP. As can be seen from Fig. 3, the adsorption quantity of Fe(III) increases with the increase of pH value in the studied pH ranges. Below pH 2.0, the adsorption quantity of Fe(III) was very low which is attributed to the protonation of the adsorbent, but the adsorption rate is increasing rapidly above pH 2.0; above pH 4.0, the adsorption quantity remained relatively constant. Owing to hydrolysis at higher pH value, pH 4 was chosen as the optimum pH for further studies. In addition, Cu(II), Co(II), Ni(II), Zn(II) and Mn(II) were not enriched by ATP–ASP at pH 4; Fe(II) could be adsorbed only to an extent of approximately 15%. Pb(II), Cd(II), Cr(III) and Hg(II) could be adsorbed by ATP–ASP in a range of 40–80% at pH 4, but they do not interfere with enrichment and determination of Fe(III). 3.2.2. Effect of the mass of adsorbent To test the effect of the mass of adsorbent on quantitative retention of Fe(III), different amounts of ATP–ASP (range from 5 to 40 mg) were added into the solution following the experimental method. The results showed that quantitative adsorption for Fe(III) was obtained in the range of 25–40 mg of ATP–ASP. Quantitative adsorption was not obtained when the mass of extractant was smaller than 25 mg. So 25 mg of ATP–ASP was selected for further studies.
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Table 1 Elution recovery (%) for Fe(III) adsorbed on ATP–ASP. Optimization of eluent concentration (the volume of HCl was 10 mL) Concentration (mol L−1 ) 0.01 0.05 Recovery (%) 27.6 64.9
0.1 90.9
0.5 100.0
1 100.3
2 99.9
Optimization of eluent volume (the concentration of HCl was 0.5 mol L−1 ) Volume (mL) 1.0 2.0 Recovery (%) 80.6 100.2
3.0 99.7
4.0 100.0
5.0 99.6
6.0 99.7
3.2.3. Effect of shaking time Shaking time is an important factor in determining the possibility of application of ATP–ASP for the selective extraction of metal ions. In this work, different shaking times (range from 5 to 40 min) were studied for the percentage extraction of Fe(III) by ATP–ASP. The results showed that the adsorption of Fe(III) was over 90% sorption during the first 10 min. It indicated that kinetics of equilibrium are very fast. The reasonably rapid kinetics of ATP–ASP–Fe(III) interaction at pH 4 reflected the high affinity and selectivity of ATP–ASP for Fe(III). We select 20 min for further studies. 3.3. Column SPE procedure 3.3.1. Effect of elution condition on recovery Since the adsorption of Fe(III) at pH < 2 is negligible, we can expect that elution will be favored in acidic solution. For this reason, various concentrations and volumes of HCl were used for the desorption of retained Fe(III). It was found from Table 1 that 2 mL of 0.50 mol L−1 HCl was sufficient for the complete elution of Fe(III). So 2 mL of 0.50 mol L−1 HCl was used as eluent in the following experiments. 3.3.2. Effect of flow rate In an SPE system, the flow rate of sample solution not only affects the recoveries of analytes, but also controls the analysis time. Therefore, the effect of the flow rate of sample solution was examined under the optimum conditions (pH, eluent, etc.) by passing 50 mL of sample solution through the microcolumn with a peristaltic pump. The flow rate was adjusted in a range of 0.5 to 5.0 mL min−1 . It was found that the retention of Fe(III) was practically not changed up to 2.5 mL min−1 flow rate. The recovery of Fe(III) decreased slightly when the flow rate is over 2.5 mL min−1 . Thus, a flow rate of 2.5 mL min−1 is employed in this work. 3.3.3. Maximum sample volume and enrichment factor To obtain reliable and reproducible analytical results and a high concentration factor, it is very important to get satisfactory recoveries for all the compounds studied in as large a volume of sample solutions as possible. So it is necessary to obtain the maximum volume in the SPE. To determine the maximum volume, different volumes of purified water at pH 4.0 were spiked with Fe(III) at 1.0 g mL −1 concentration levels. Following the experimental procedure, the recoveries of analyte at different volumes were obtained. The results showed that the maximum sample volume could be up to 400 mL with the recovery >95%. Therefore, 400 mL of sample solution was adopted for the preconcentration of Fe(III) from sample solutions. A high enrichment factor of 200
Fig. 4. Effect of initial volume (V0 ) of Fe(III) on the adsorption quantity (Q) of ATP–ASP. pH 4.0; sample concentration 10 g mL−1 ; temperature 25 ◦ C.
was obtained because 2.0 mL of 0.5 mol L−1 HCl was used as eluent in these experiments. 3.4. Adsorption capacity The adsorption capacity is an important factor because it determines how much adsorbent is required to quantitatively concentrate the analytes from a given solution. The adsorption capacity was tested following the general procedure. To measure the static adsorption capacity, 50 mg of adsorbent was treated with 10.0 g mL−1 of various volumes of Fe(III) solutions adjusted with 0.1 mol L−1 of HCl or NH3 at pH 4. As can be seen in Fig. 4, the amount of Fe(III) adsorbed per unit mass of ATP–ASP increased with the initial volume of Fe(III). The initial volume of Fe(III) was increased till the plateau values (adsorption capacity values) were obtained. The static adsorption capacity of ATP–ASP for Fe(III) was calculated as 33.63 mg g−1 . However, Fe(III) was adsorbed poorly on untreated attapulgite and ATPAP at pH 4. The adsorption capacity and enrichment factor of ATP–ASP for Fe(III) were also compared with those of other important matrices used for the separation and preconcentration (Table 2). As seen from the data, ATP–ASP had relatively high capacity and enrichment factor values compared to other methods reported. 3.5. Effects of coexisting ions The effects of common coexisting ions on the adsorption of Fe(III) on ATP–ASP were investigated. In these experiments, solu-
Table 2 Comparison of adsorption capacity and enrichment factor of some adsorbents used for the separation and preconcentration of Fe(III). Adsorbent
Complexing media
Capacity
Enrichment factor
Reference
Nanometer SiO2 Multiwalled carbon nanotubes Silica gel Naphthalene Sepiolite Attapulgite
P-dimethylamino benzaldehyde Ethylenediamine Curcumin Methylthymol blue Escherichia coli Asparagine
14.7 mg g−1 28.69 mg g−1 0.46 mmol g−1 0.10 mg g−1 0.098 mmol g−1 33.63 mg g−1 (0.60 mmol g−1 )
100 200 75 100 50 200
[23] [24] [25] [26] [27] Present work
Z. Zang et al. / Analytica Chimica Acta 663 (2010) 213–217 Table 3 Analysis results for the determination of Fe(III) in standard reference materials (GBW 08301, river sediment; GBW 08504, cabbage) and biological samples. Analyte
Measured (g g-1 )a
Certified (g g-1 )
GBW08301 GBW08504 Balsam pear leaves
39.8 ± 1.3 52.1 ± 1.8 3.58 ± 0.22
39.4 ± 0.12 52.0 ± 3.2 3.56 ± 0.17
a
The value following “ ± ” is the standard deviation (n = 3).
Table 4 Analytical results for the determination of Fe(III) in Yellow River and tap water samples. Ion
Added
Founda
0
4.32 ± 0.05 9.54 ± 0.16 14.51 ± 0.07 0.13 ± 0.05 5.11 ± 0.06 10.05 ± 0.10
Recovery (%)
−1
Fe (III) (g mL ) Yellow River water
Tap water
a
5 10 0 5 10
102.4 101.3 99.6 99.2
The value following “ ± ” is the standard deviation (n = 5).
tions of 1.0 g mL−1 of Fe(III) containing the added interfering ions were treated according to the recommended procedure. The tolerance limit was set as the amount of ions causing recoveries of the analyte to be less than 90%. The results showed that in excess of 2000-fold K(I), Na(I), Ca(II) and Mg(II), 100-fold Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Cr(III), Pb(II) and Hg(II) ions had no significant interferences in the preconcentration and determination of Fe(III). This is due to the low adsorbing capacity or rates for interfering ions. It can be seen that the presence of major coexisting ions has no obvious influence on the determination of Fe(III) under the selected conditions. 3.6. Detection limits and precision Under the optimal conditions, eight portions of standard solutions were enriched and analyzed simultaneously following the recommended procedure. The relative standard deviation (RSD) of the method was 3.4%, which indicated that the method has good precision for the analysis of trace Fe(III) in solution samples. In accordance with the definition of IUPAC, the detection limit of the method was calculated based on three times the standard deviation of eight runs of the blank solution. The detection limit (3) of the proposed method was 0.19 g L−1 . 3.7. Application of the method The proposed method has been applied to the determination of trace Fe(III) in standard materials (GBW 08301, river sediment; GBW 08504, cabbage), balsam pear leaves, tap water and Yellow River water samples. The results are listed in Tables 3 and 4. The
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analytical results for the standard materials were in good agreement with the certified values. The analytical results for balsam pear leaves were in agreement with the electrothermal atomic absorption spectrometry (ET-AAS) method. For the analysis of natural Yellow River water and tap water samples, the standard addition method was used. The recoveries of analyte were in the range of 99–103%. These results indicated the suitability of ATP–ASP for selective SPE and determination of trace Fe(III) in environmental samples. 4. Conclusions In this study, the proposed selective and sensitive method for the determination of trace Fe(III) was developed by using asparagine modified attapulgite as solid-phase extractant. The preparation of asparagine modified attapulgite sorbent was relatively simple and rapid. This new adsorbent had higher adsorption capacity and selectivity for Fe(III), and the method was successfully applied to the analysis of trace Fe(III) in biological and water samples. The precision and accuracy of the method are satisfactory. References [1] J.H. Martin, S.E. Fritzwater, Nature 331 (1988) 342–343. [2] K. Pyrzynska, Crit. Rev. Anal. Chem. 29 (1999) 313–321. [3] C.F. Poole, New trends in solid-phase extraction, Trends Anal. Chem. 22 (2003) 362–373. [4] J.R. Dean, Extraction Methods for Environmental Analysis, Wiley, New York, 1998. [5] R. Giustetto, F.X.L. Xamena, G. Ricchiardi, S. Bordiga, A. Damin, R. Gobetto, M.R. Chierotti, J. Phys. Chem. B 109 (2005) 19360–19368. [6] J. Huang, Y. Liu, Q. Jin, X. Wang, J. Yang, J. Hazard. Mater. 143 (2007) 541–548. [7] A. Neaman, A. Singer, Appl. Clay Sci. 25 (2004) 121–124. [8] E. Álvarez-Ayuso, A. García-Sánchez, J. Hazard. Mater. 147 (2007) 594–600. [9] H. Chen, A.Q. Wang, J. Colloid Interface Sci. 307 (2007) 309–316. [10] H. Chen, Y.G. Zhao, A.Q. Wang, J. Hazard. Mater. 149 (2007) 346–354. [11] W.J. Wang, H. Chen, A.Q. Wang, Sep. Purif. Technol. 55 (2007) 157–164. [12] H.H. Murray, Appl. Clay Sci. 17 (2000) 207–211. [13] K. Boki, K. Sakaguchi, H. Tomioka, JJTHE 41 (1995) 426–432. [14] P. Liu, T.M. Wang, J. Hazard. Mater. 149 (2007) 75–79. [15] Q.H. Fan, D.D. Shao, J. Hu, W.S. Wu, X.K. Wang, Surf. Sci. 602 (2008) 778–785. [16] Y.J. Zhao, Y. Chen, M.S. Li, S.Y. Zhou, A.L. Xue, W.H. Xing, J. Hazard. Mater. 171 (2009) 640–646. [17] D.P.H. Laxen, R.M. Harrison, Anal. Chem. 53 (1981) 345–350. [18] E.S. Miranda Carlos, B.F. Reis, N. Baccan, A.P. Packer, M.F. Gine, Anal. Chim. Acta 453 (2002) 301–310. [19] Y.W. Liu, X.J. Chang, Y. Guo, S.M. Meng, J. Hazard. Mater. B 135 (2006) 389–394. [20] Z.W. Niu, Q.H. Fan, W.H. Wang, J.Z. Xu, L. Chen, W.S. Wu, Appl. Radiat. Isot. 67 (2009) 1582–1590. [21] H.T. Tang, Organic Compound Spectra Determination, Publishing house of Beijing University, Beijing, 1992, pp. 124-159. [22] Q.N. Dong, IR Spectrum Method, Publishing house of the Chemical Industry, Beijing, 1979, pp. 104–168. [23] Y.M. Cui, X.J. Chang, Y.H. Zhai, X.B. Zhu, H. Zheng, N. Lian, Microchem. J. 83 (2006) 35–41. [24] Z.P. Zang, Z. Hu, Z.H. Li, Q. He, X.J. Chang, J. Hazard. Mater. 172 (2009) 958–963. [25] X.B. Zhu, X.J. Chang, Y.M. Cui, X.J. Zou, D. Yang, Z. Hu, Microchem. J. 86 (2007) 189–194. [26] N. Pourreza, R. Hoveizavi, Anal. Chim. Acta 549 (2005) 124–128. [27] H. Bag, A.R. Turker, M. Lale, Talanta 51 (2000) 1035–1043.